Television apparatus



`RD. KELL j TELEVI S ION APPARATUS .NIE

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July 18,A 1939. R. D. KELL 2,166,688

TELEVISION APPARATUS Filed Dec. 18, 1937 3 Sheets-Sheet 2 U Uv .U

[C2 f/ K Y Snventor Gttomeg Juiy 18, 1939.

R. D. KELL TELEVISION APPARATUS Filed Dec. 18,

1937 5 Sheets-Sheet 3 'N z' v6o N Ii 'Zinnentor Mittel-neg Patented July 18, 1939 PATENT OFFICE 2,166,686 TELEVISION APPARATUS Ray D. Kell, Haddoneld, N. J., assignor to Radio Corporation oi' America, a corporation of Del- Application December 18, 1937, Serial No. 180,502

7 Claims.

My invention relates to the production oi' electrical impulses having a certain desired wave shape, and particularly to a method and apparatus for producing synchronizing impulses for use in a television system.

In application Serial No. 180,493, led December 18, 1937, in the name of A. V. Bedford, entitled Television systems and assigned to the Radio Corporation of America, there is described and claimed a television system in which one group of synchronizing impulses `(the horizontal impulses, for example) have ya steep front side and a gradually sloping back side, while the other group of synchronizing impulses (the vertical or framing impulses, for example) have a steep back side and a gradually sloping front side. These synchronizing impulses are passed through a differentiating circuit in the television receiver whereby a steep "front" produces a sharp impulse of one polarity and a steep back produces a sharp impulse of the opposite polarity. Thus, the horizontal and vertical synchronizing impulses may be separated bv` ampli- 'tude selection (as by the use of clipping tubes) for holding the horizontal and vertical deflecting circuits of the receiver in synchronism with scanning at the transmitter. An object of my invention is to provide an improved method of and means for producing synchronizing impulses of the above-described character.

A further object of -my invention is to provide an improved method of and means for producing electrical impulses which have one side substantially perpendicular, while the other sideis grad-I ually sloping.

In a preferred embodiment of my invention, the desired impulse is obtained by producing a rectangular impulse and a saw-tooth wave and adding them whereby a portion of the combined Wave appears as an impulse with perpendicular sides and a sloping top. .The combined wave is then clipped at a level such that only the upper part of this portion with the sloping top appears in the output circuit. 'I'he result is an impulse with one very steep side and one gradually sloping side.

Whether the steep side of an impulse is' the front side or the back side is determined by whether the rectangular impulse is added on the back side or the front side-of the saw-tooth wave. The relation of the rectangular impulse with respect to the saw-tooth wave may be determined by the amount either the rectangular impulse or the sW-tooth wave is delayed before the two are adde (ci. 25o-'36) and Figure 4 is a group of curves showing the complete synchronizing signal.

Referring to Fig. 1, I have shown one embodi- .the vertical synchronizing impulses are obtained,

ment of myinvention as applied to a television system which produces a 441-line interlaced picture. It will be understood that the apparatus shown in Fig. 1 is located at the television transmitter and supplies horizontal and vertical synchronizing impulses to the deiiecting circuits of 20 both the cathode ray transmitter tubeA and the cathode ray tube at the receiver.

'I'he horizontal and vertical synchronizing impulses are derived from a common source such as a multivibrator or other suitable oscillator i.

A second multivibrator 2 divides the frequency of the oscillator l by two to produce impulses at the line frequency, 13,230 cycles per second in the specific system being described.

A chain of muitivibratcrs s, 4 and s divide the 30 frequency of oscillator I to produce impulses occurring at the picture frame frequency of 60 per second. It will be understood that the 60 cycle and 13,230 cycle impulses having the desired odd-.line relationship for interlacing may be obtained in any other suitable way, as by means of a rotating disc having suitable openings therein,

.as described and claimed in Patent No. 2,152,234

issued in the name of R.. C. Ballard, and assigned to the Radio Corporation of America, or by 40 means of blocking oscillators as described and claimed in application Serial No. 726,258, led May 18, 1934, in the name of A. V. Bedford, entitled Television systems, and assigned to the Radio Corporation of America.

The portion of the circuit which produces the horizontalvsynchronizing impulses will first be described. The saw-tooth voltage wave, which is to be combined with a rectangular impulse, is produced in this specic example by supplying a rectangular voltage impulse, indicated at 5, from 1f' the oscillator 2, over a conductor 'i and through a resistor 8 to a condenser 9. The condenser 9 is connected across the input electrodes of a screen grid tube e and is shunted by a resistor I I,

the resistor II having a high resistance. such as one megohm, as compared with the resistance oi' resistor l. In practice, the resistor 8 may be the plate impedance of one of the multivibrator tubes. i

Condenser 8 is. alternately charged and/discharged a small amount through resistor 8, whereby a saw-tooth voltage wave, indicated at I2, is impressed upon the control grid of tube e. Stated differently, the circuit 8, Il integrates the impulses 5 to produce the saw-tooth wave I2.

'I'he rectangular voltage which is to be combined with the saw-tooth wave is produced in this specic example by supplying rectangular voltage impulses, indicated at I0, from oscillator 2 to a vacuum tube c through a diilerentiating circuit comprising a condenser I3 of. small capacity and a resistor Il o! comparatively low resistance, the resistor I4 being connected across the input electrodes of the tube c. It will be understood that impulses lloccur at the rate of 13,230 per second. A differentiating circuit of this character and its action are described land claimed in Patent No. 2,132,655, granted October 11, 1938 to J. P. Smith, entitled System for producin'g electrical impulses, and assigned to the Radio Corporation of America.

The derivative of impulse I0 appears lon the grido! tube c, as indicated at I8. Since tube c is adjusted to act as a clipping tube, only the upper impulse portion of wave I8 passes through the tube. This portion appears inverted in the plate circuit of tube c, as indicated at I'I, and is impressed upon a clipping tube d whereby a square topped voltage wave appears in the output of tube d, as indicated at I8. It will be noted that, by diierentiating and clipping, the impulse 5 has been narrowed but not delayed.

The tubes c and d, and other clipping tubes to be described, are'adjusted to function as.clip ping tubes by selecting such values for the grid condensers and grid leak resistors that the tubes are grid leak biased. That is, the charge on the grid condenser holds over /a substantial amount between rectangular impulses to bias the tubes negatively the desired amount. as described in the above mentioned Smith application. y

Impulses I8 are combined, with the saw-tooth waves I2 after impulses I8 have been suitably delayed in a delay network I9 to,make the two groups of signals combine in the correct time relation. The desired addition of signals is obtained by impressing the delayed impulses I8 upon the screen grid of tube e. The combined signal, after being inverted by a tube f, is of the character indicated at 2|.

Signal 2| is supplied to a clipping tube a, which .clips signal 2| at the level indicated by the dotted line to produce the desired impulse, indicated at 22, having asteep front side and a gradually sloping back side.

The delay network I9 may be of any suitable design, such as a conventional capacity-inductance network of recurrent sections, or it may be a network comprising vacuum tubes andwave` shaping networks of the character described in the above mentioned Smith application Serial No. 8,659.

Referring now to that portion of the circuit which produces the vertical synchronizing impulses having a steep back side and a sloping kont side, rectangular voltage impulses occurring at the framing frequency oi' 60 cycles per second and indicated at 25 are supplied from oscillator 8 over a conductor 2l, through a resistor 21 to a condenser 23 which is connected across the input electrodes of vacuum tube e'. Condenser 28 is shunted by a resistor 28 having comparatively high resistance. Thus, a saw-tooth voltage wave is supplied to the grid of tube e' as indicated at 3l. It will be seen that tube e' corresponds to tube e in the horizontal synchronizing circuit. Similarly, the vacuum tubes c', d', f' and a now to be described correspond to tubes c, d, f and p in the horizontal synchronizing circuit.

The rectangular voltage impulse to be addedl to the saw-tooth 3| Ais obtained by taking from oscillator 6 a rectangular voltage impulse indicated at 32, which occurs at the frame frequency of per second, and supplying it to a difierentiating circuit comprising a condenser 33 of small capacity and a resistor 34 ot comparatively small resistance. 'I'he resulting signal indicated at 36 appearing on the grid of tube c' is clipped by tube c as indicated by the dotted line, and after iurther clipping by tube d', appears in the plate circuit of tube d as a narrowed rectangular impulse indicated at 31.

Impulses 31 are delayed by a delay network 38 which may be of the same type as delay network i8. The delayed impulses 31 are added to the saw-tooth waves 3| by impressing them upon the screen grid of tube e'. The amount that impulses 31 are delayed is such as to make them add on the iront side of the saw-tooth wave rather than on the back side, as is the case in the horizontal synchronizing circuit. Thus, after being inverted by tube f', the combined signal appears in the output circuit of tube f', as indicated at 39. This signal is then clipped by the tube a', as indicated by the dotted line, to produce the desired signal having a steep back side and a. sloping front side, as shown at 4I.

The vertical synchronizing signals 4I and the horizontal synchronizing signals 22 are combined in the common plate circuit of tubes a and g', the combined signals then have their sharp peaks clipped oil by a clipping tube h whereby there appears in the output circuit of. tube h a signal of the character shown at 42 and shown more clearly in Fig. 4.

In Fig. 4, the curve marked odd and the curve marked even represent the same signal (the output of tube h) but the even" signal qccurs 1,60 second later than the odd signal. The signals 22 and II are thehorizontal and vertical synchronizing impulses, respectively. From a comparison of these two curves, it will be seen that the steep sides of the even horizontal impulses are displaced t scanning li'ne with respect to the steep sides of the odd" horizontal impulses whereby an interlaced picture is produced.

The way in which the horizontal synchronizing signals are produced will be better understood by referring to Fig. 2, where the time relation of the several signals is shown. curves corresponding to those in Fig. 1 having the same reference numerals.

It will be seen that the desired final impulses 22 are obtained by adding the rectangular impulses I8 (derived from impulses 5) and the sawtooth waves I2 in suchtime relation that, after the combined signal 2| hasbeen clipped at the level indicated by the dotted line, the resulting signal 22 has a steep front" and a sloping back. It will be apparent, by comparing the impulses I8 and the combined signal 2|, that the impulses I8 are delayed enough to make them i'all on the back side of the saw-tooth wave I2.

Also referring to Fig. 3, there is shown the time relation of the several signals which are produced to obtain the vertical synchronizing irnpulses. In this gure, curves corresponding to those in Fig. 1 are indicated by the same reference numerals. An inspection of curve 39 shows that the rectangular impulse is delayed just enough to make it fall on the front side of the sawtooth, rather than ,on the "back side of the saw-tooth as in Fig. 2, whereby the combined signal may be clipped at the level indicated by the dotted line to produce the vertical synchronizing impulses 4I having a steep back side and a gradually sloping front side.

While I have shown andv described one way of producing saw-tooth waves and one way of producing rectangular impulses, it is to be understood that such waves and impulses may be produced in any suitable manner.

Instead of having the saw-tooth waves I2 occur at the horizontal deiiecting frequency, they may be produced at a multiple frequency. For example, the conductor 'I may be switched to a conductor 45 leading to the main oscillator I,

whereby saw-tooth waves occurring at the rate of 26,460 per second are supplied to the tube e. In this case an impulse I8 is added to every other saw-tooth wave, instead of to every saw-tooth wave.

It may be noted that generallythe duration oi' the impulse I8 in the horizontal synchronizing circuit is made approximately the same as the duration of the impulse 31 in the vertical synchronizing circuit, although-of course; this is not essential.

It` will be understood that while I have described my invention as applied to an interlaced scanning system, it is not so limited. As indicated in Fig. 4, if the system is designed to provide the so-called "odd-line interlaced scanning described, the steep sides of the horizontal synchronizing impulses occurringat time Tri-V30 sec.

` should fall half-way between the steep sides of the horizontal synchronizing impulses occurring at T1 sec.

I claim as my invention:

1. The method of producing periodically recurring impulses each having a front side which has a different slope than its back side, said method comprising producing an impulse having a back side of a certain slope, producing an impulse having a front side oi.' a different slope, combining said impulses to produce a combined wave which has a portion having a back side with l a slope determined by said certain slope and having a front side with a slope determined by said different slope, and passing only said portion to an output circuit.

2. The method of producing recurring impulses each having a front side and a back side, one side being steeper than the other side, said method comprising producing saw-tooth waves, producing substantially rectangular waves, combining said saw-tooth waves and said rectangular waves whereby a portion of the combined wave has a greater amplitude than the saw-tooth wave, and passing only said portion to a utilization circuit.

3. The method of producing synchronizing impulses which comprises producing saw-tooth waves each ha'ving a front side and a back side, producing substantially rectangular impulses each having a duration less than that o! one side of greater amplitude than said saw-tooth waves,

' ofsaid saw-tooth waves, combining said waves and said impulses to produce a combined portion and passing only said portion to a utilization ciry pulses each having a duration less than that of one of said rsaw-toothwaves and of such amplitude that when combined with said saw-tooth waves portions of greater amplitude than the amplitude of said saw-tooth waves are produced, combining said Waves and said impulses and passing only said portions to a utilization circuit.

5.A generator of periodically recurring impulses comprising means for producing periodically recurring impulses each having a front side and a back side, one of said sides having a certainV slope, means for producing other periodically recurring impulses each having a front side and a back side, the side opposite 'said one side having a slope diierent than said certain slope, means for adding said iirst mentioned impulses and said second mentioned impulses Whereby a combined wave is produced having a portion withone side which has a slope determined by said certain slope and with the opposite side having a slope determined by said different slope, and means for passingonly said portion to an output circuit.

6. A generator of synchronizing impulses comprising means for producing saw-tooth waves each having a front side and a back side, means for producing substantially rectangular impulses each having a duration less than one side of one of said saw-tooth waves, means for so combining said waves and said impulses that said impulses add on one side of said waves to produce periodically recurring portions each having a slope on one side determined by said saw-tooth waves and a slope on the other side determined by said impulses, and means for passing only said portions' toan output circuit.

7. In a television transmitter, a generator of comparatively high frequency horizontal synchronizing impulses and .of comparatively low frequency vertical synchronizing impulses, `said generator comprising means for generating sawtooth waves occurring at a rate at least as high as said high frequency, each of said waves having a front slopeV and anback slope, means for generating substantially rectangular impulses of less duration than one of said slopes, means for adding said impulses to said saw-tooth waves in such relation that each impulse falls on said one slope of a saw-tooth wave to produce a combined portion of greater amplitude than that of the'sawtooth waves, means for passing only said portion to an output circuit, means for generating sawtooth waves occurring at a rate at least as high as said low frequency, each of said low frequency 

